An antenna array is an antenna array formed by feeding and spatially arranging, according to a requirement, two or more antennas working at a same frequency, for example, for a phased array antenna (Phased Array Antenna, PAA), relative phases of feeding signals are changed, so as to achieve an objective of spatial beam scanning. In a phased array system in which frequency division duplex (Frequency Division Duplex, FDD) is used and receiving and transmitting of a signal use different antennas or different PAAs, based on a size requirement of the system, a distance between transmit and receive antennas (arrays) is relatively small; therefore, in this case, isolation between the two antennas (arrays) can hardly satisfy the requirement of the system, thereby causing that signal interference between the transmit antenna (array) and the receive antenna (array) is relatively large, which cannot satisfy a normal operation requirement of the system.
In the prior art, the following solutions are mostly used to increase isolation between antennas (arrays), but all the solutions can hardly satisfy an entire requirement of a system. (1) A unit gain of an antenna (array) is increased, where the increase in the gain of the antenna can increase isolation to some extent, but cannot satisfy an requirement imposed by a phased array system on an angle of spatial beam scanning, and a size of the antenna needs to be increased at the same time, which leads to an increase in a size of the system; therefore, a size requirement of the system cannot be satisfied; (2) A distance between transmit and receive antennas (arrays) is increased, where due to a limitation of the size requirement of the phased array system, the increase in the distance between the transmit and receive antennas (arrays) cannot satisfy the requirement either; and (3) An appropriate filter is disposed at a rear end of a receive antenna (array), where disposing of more filters not only may increase costs of the system, but also may occupy more area of a radio frequency board, so that the size of the system cannot be controlled to be within an expected range. Therefore, the existing solutions of increasing isolation of an antenna (array) cannot satisfy an actual requirement.